Method and apparatus to detect nanometer particles in ultra pure liquids using acoustic microcavitation

Abstract

An apparatus to produce acoustic cavitation by controlling cavitation events in a liquid insonification medium utilizing a waveform to excite a transducer with a series of bipolar inharmonic tone bursts having medium recovery intervals between respective bursts so that the medium repeatedly recovers from cavitation events between bursts. The apparatus may be used to clean a semiconductor wafer, to de-coat a painted surface having, to induce a chemical reaction, and/or to provide recycled paper made from inked paper de-inked by cavitation. Cavitation events are generated using a transducer and a waveform generator, e.g., square wave tone bursts, to excite the transducer with a signal controlled in frequency, burst repetition rate, duty-cycle and/or amplitude, e.g., utilizing bursts having a frequency between 500 KHz and 10 MHz, and a duty cycle between 0.1% and 70%.

1. A particle detector utilizing an acoustically induced cavitation event to detect presence of a particle suspended within an ultrapure liquid, said detector comprising a resonant mode transducer module that operates in a thickness direction; a communicating path between said transducer module and a region of said particle thereby establishing an acoustic coupling between the transducer module and said particle; an excitation source that supplies said transducer module with a waveform comprising a series of bipolar inharmonic tone burst signals having on and off burst intervals thereby to produce an acoustic cavitation field in the region of said particle whereby to effect said cavitation event about said particle; and a controller to control at least one of duty cycle, frequency, and amplitude of said bipolar inharmonic tone burst signals to control said cavitation event about said particle whereby to enable detection of said particle. 
     
     
       2. The particle detector of  claim 1 , wherein said transducer module detects an acoustic echo created by said cavitation event about said particle during an off period of said on and off burst intervals. 
     
     
       3. The particle detector of  claim 2 , wherein the amplitude of said bipolar inharmonic tone burst signals is set to a level to effect vacuous cavitation about said particle. 
     
     
       4. The particle detector of  claim 2  wherein said inharmonic tone burst signals comprise bursts of square waves. 
     
     
       5. The particle detector of  claim 4  wherein said transducer module is shaped to focus acoustic energy in said region of said particle. 
     
     
       6. The particle detector of  claim 4  wherein said transducer module is concaved to focus acoustic energy in said region of said particle. 
     
     
       7. A particle detector utilizing cavitation events associated with particles suspended in an ultrapure liquid medium to detect said particles, said particle detector comprising:
 (a) at least one transducer module to produces acoustic field emissions, 
 (b) a source of power that powers the transducer module with a bi-polar, inharmonic tone burst waveform having a duty cycle that provides on-off burst intervals, said source of power being applied to said transducer module to produce in said medium a cavitation region having multiple high frequency and multiple lower frequency acoustic field components, and 
 (c) an echo detector to detect cavitation events associated with said particles during off periods of said on-off burst intervals whereby to detect said particles. 
 
     
     
       8. The particle detector of  claim 7 , wherein said transducer module provides said echo detector. 
     
     
       9. The particle detector of  claim 7 , wherein said inharmonic tone burst waveform comprises bursts of square waves. 
     
     
       10. The particle detector of  claims 9 , further comprising a controller that controls at least one of duty cycle, amplitude, tone burst repetition rate, and frequency of said waveform in order to achieve a desired level of cavitation and particle detection. 
     
     
       11. An apparatus to produce vacuous cavitation about particles suspended in a liquid medium in order to detect said particles, said apparatus comprising a transducer, an energizing source that powers the transducer with a bipolar inharmonic tone burst signal to produce an acoustic field in said medium wherein said tone burst signal has a duty cycle that defines on and off burst intervals to produce a cavitation region in the medium having multiple high frequency and multiple lower frequency acoustic field components, and a controller that controls at least one of duty cycle, amplitude, and frequency of said bipolar inharmonic tone burst signal according to a desired level of vacuous cavitation and particle detection. 
     
     
       12. An apparatus that produces acoustically induced cavitation events relative to a particle suspended in a liquid insonification medium, said apparatus comprising a single-transducer resonant mode transducer module that operates in a thickness direction; a communicating path between said transducer module and a region of said particle thereby to establish an acoustic coupling between the transducer module and the particle; an excitation source that supplies said transducer module with a waveform comprising a series of bipolar inharmonic tone burst signals having on and off burst intervals to produce within the medium about the particle an acoustic cavitation field; and a controller to control at least one of duty cycle, frequency, and amplitude of said bipolar inharmonic tone burst signals to effect induction of vacuous cavitation within said insonification medium about said particle. 
     
     
       13. The apparatus of  claim 12  further including an impedance-matched layer between the transducer and the medium. 
     
     
       14. The apparatus as recited in  claim 13 , wherein said series of bipolar inharmonic tone burst signals comprise a series of square wave bursts. 
     
     
       15. The apparatus as recited in  claim 14 , wherein said controller controls the duty cycle of said tone bursts between 0.1 and 2%. 
     
     
       16. The apparatus as recited in  claim 14 , wherein said controller controls the duty cycle of said tone bursts up to 70%. 
     
     
       17. A method of detecting a particle in an ultrapure liquid comprising:
 providing a transducer module to produce acoustic field emissions in said ultrapure liquid, 
 powering said transducer module with a bi-polar, inharmonic tone burst waveform having a duty cycle that provides on-off burst intervals to produce in said medium a cavitation region having multiple high frequency and multiple lower frequency acoustic field components, and 
 detecting cavitation events associated with said particles during off periods of said on-off burst intervals whereby to detect said particles. 
 
     
     
       18. The method of  claim 17 , further comprising:
 controlling at least one of duty cycle, frequency, and amplitude of said bipolar inharmonic tone burst signals to induce cavitation within said insonification medium about said particle. 
 
     
     
       19. The method of  claim 18 , further comprising controlling said tone burst signals to induce vacuous cavitation. 
     
     
       20. The method of  claim 18 , further comprising powering said transducer with square wave tone burst signals. 
     
     
       21. The method of  claim 18 , further comprising controlling the duty cycle of said tone bursts between 0.1 and 2%. 
     
     
       22. The method of  claim 18 , further comprising controlling the duty cycle of said tone bursts up to 70%.